This invention relates to a fog detecting apparatus, and more particularly to a fog detecting apparatus for use in a vehicle, using optoelectronic system.
It is known that various types of fog detecting apparatus, which detect the fogging condition on a windshield of a vehicle, are employed and a fog removing apparatus such as a defroster is provided in the vehicle for preventing a traffic accident caused by the poor visibility.
In one type of such apparatus, an optoelectronic system is used, such as is disclosed in Japanese Utility Model Publication No. 55-3408, comprising light-emitting means actuated in response to a signal from an emitting control circuit, and light-receiving means for receiving the light emitted from the light-emitting means and for producing an electrical signal being in proportion to the intensity of the received light. The fogging condition on the windshield is detected on the basis of the electrical signal.
On the other hand, it is intended that the fog removing apparatus is automatically controlled according to the electrical signal so as to adequately remove the fog from the windshield.
However, it is actually difficult to produce the electrical signal corresponding to the fogging condition accurately due to a secular change and the contamination of the optoelectronic system or the like, and thereby adequate control of the fog removing apparatus is not ensured.
Furthermore, because of the disproportion of the fogging condition on the windshield, although the fog removing apparatus has been actuated according to the electrical signal, the fog existing on portions of the windshield required for a safe drive is not completely removed and some of the fog may remain. Namely, when the fogging is detected at the detecting portion of the windshield, the fog removing apparatus is arranged to be actuated, and when the fogging thereat is removed, the fog removing apparatus is arranged to be stopped no matter whether all fog is actually removed or not.
Still furthermore, in the case that the fog is not completely removed, a period fogged again becomes shorter and the cycle of actuation and stopping of the fog removing apparatus becomes shorter, resulting in an uncomfortable driving of the vehicle.